The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time, computer systems have evolved into extremely sophisticated devices, and computer systems may be found in many different settings. Computer systems typically include a combination of hardware, such as semiconductors and printed circuit boards, and software, also known as computer programs.
Printed circuit boards typically contain discrete elements (such as chips, transistors, resistors, capacitors, and inductors) connected by bonding metallic wires, often called transmission lines. These transmission lines play a significant role in determining important characteristics of the printed circuit board, such as the size, power consumption, speed, reliability, and clock frequency of the printed circuit board. Because the transmission lines are so important, developers of printed circuit boards study the impact of the transmission lines on the aforementioned characteristics prior to actually manufacturing the printed circuit board. One way to accomplish this study is via a transmission line model.
For a transmission line model to be useful, it must accurately represent the actual printed circuit board that will eventually be manufactured. This accuracy can be compromised when a buyer uses multiple suppliers of printed circuit boards. Each supplier has its own unique manufacturing process and its own unique set of manufacturing tolerances, which can cause differences in the transmission line characteristics of printed circuit boards produced by different suppliers. Despite the problems that these differences can cause, buyers wish to use multiple suppliers in order to reduce the cost and risk exposure in the production and procurement of the printed circuit boards used in the building of a computer or other electronic device.
Thus, the developer of the transmission line model needs to account for the differences in printed circuit boards that may come from multiple suppliers. Typically, model developers have developed worst-case models, which cover the extreme values of manufacturing and material tolerances from the multiple vendors. These worst-case models have led to transmission line models that are generally overly conservative, sacrificing valuable performance and risking increased cost.
Without a better way to design a printed circuit board that is optimal instead of worst-case, printed circuit boards will continue to suffer from lowered performance and increased cost. Although the aforementioned problems have been described in the context of printed circuit boards, they apply equally to any other environment where transmission lines are modeled, such as flex cables, coaxial cables, chip packages, organic chip carriers, and fiber optics.